1. Field of the Invention
The present invention relates to a communication error detecting method for a bus communication network in a vehicle.
2. Background Art
In general, a plurality of electronic control units (ECU's) are installed on a vehicle for electronically controlling a plurality of actuators, respectively. Each ECU is designed to electronically control an actuator connected to the subject ECU while transmitting and receiving data between the subject ECU and a corresponding ECU through a communication via a multiplex transmission pathway.
When there occurs an abnormality in the ECU's or the multiplex transmission pathway in such a vehicle multiplex communication system, data transmission cannot be performed or is inappropriately performed between the ECU's. Accordingly, there is a fear that a proper electronic control will not be performed. To deal with this, generally, each ECU is provided with a communication error detecting function for determining the existence of an abnormality in the corresponding ECU or the transmission pathway. For example, as described in JP-UM-B-7-23722, each ECU is designed to determine that an abnormality has occurred in the corresponding ECU or the transmission pathway when the subject ECU cannot receive data from the corresponding ECU over a predetermined period of time or longer.
Here, these ECU's constituting the vehicle multiplex communication system are generally divided into the ECU's which are powered on whether the ignition key is situated at the OFF position or the ON position and the ECU's which are powered on only when the ignition key is situated at the ON position. Since the latter ECU's are kept inoperative while the ignition key remains at the OFF position and hence no transmission of data is enabled, in case a communication detection is performed by the former ECU which can be operative even when the ignition key is situated at the OFF position, there may occur a case where the latter ECU is erroneously determined to have failed. Then, conventionally, the communication error detection is designed to be stopped when the ignition key is situated at the OFF position so as to prevent the occurrence of such an erroneous determination.
On the other hand, with a view to reducing the load of a battery at the time of cranking, there occurs sometimes a case where a multiplex communication system is configured in which part of the ECU's are powered off when the ignition key is situated at a cranking position. In the following description, an ECU which is powered on even at the time of cranking is referred to as a first type ECU and an ECU which is powered off at the time of cranking is referred to as a second type ECU.
In the multiplex communication system configured as described above, there exist first type ECU's and second type ECU's in a mixed fashion. Since a communication error detection is performed by the first type ECU when the ignition key is situated at the cranking position (which, broadly speaking, corresponds to the ON position), even if there is provided a countermeasures is taken to stop the communication error detection when the ignition key is situated at the OFF position, there may be caused a risk that the second type ECU is determined to have failed.